From Ken Turkowski Consulting:
DeFish is an application that can be useful in constructing environment maps from photographs taken with fisheye lenses. This application makes use of technology that was widely published in 1986, 5 years before any fisheye patents.
The intent is to provide enough capability to project a fisheye image to a perspective image, thereby allowing the user to use the perspective images in other environment map authoring software, such as Apple's QuickTime VR Authoring Studio. The primary advantage to this technique is to capture a much larger field of view than that
This software has been tested on a variety of fisheye images, from 16 mm to 6 mm equivalents. It is simple to calibrate for center and radius by clicking and dragging. A provision is made for barrel distortion correction, but I'm afraid it isn't very easy for even the expert to use; this is something for a future revision.